Aluminum electrolytic capacitors are constructed as a stack of layers of a cathode foil, which may be, for example, a thin, roughened Al foil having a thickness between 20 and 50 μm, and of an anode foil, which may be, for example, a roughened Al foil around 100 μm thick, and which has a dielectrically operative oxide layer that is deposited on the foil by an electrochemical process. The cathode foil too has a thin oxide layer, around 1.5-3 nm thick. The stack of layers is usually present in the form of a coil wound around a mandrel, which is built into an aluminum cup.
Between the foils there is a course of one or more layers of paper, which is impregnated with the operating electrolyte. This operating electrolyte constitutes the actual cathode.
Operating electrolytes of the type named at the beginning that also contain ammonium benzoate are known. German Patent 693 04 732 Part 2 discloses an electrolyte that contains benzoic acid or its ammonium salts and additional aliphatic dicarboxylic or tricarboxylic acids together with solvents, which include ethylene glycol and other alcohols. These operating electrolytes have the disadvantage of a low sparking voltage of about 300 V. Consequently, the aluminum electrolytic capacitors made with the known operating electrolytes are not suitable for operation with higher voltages.